Insulinoma

Insulinoma refers to a mass that secretes insulin. These tumors arise from the pancreatic beta cells and are considered functional tumors, meaning they produce a hormone—here, insulin. Insulinomas can occur in both dogs and cats.

Uncontrolled insulin secretion causes low blood glucose. Low glucose can lead to neurologic signs, including:

• seizures
• collapse
• generalized weakness
• dull mentation

Diagnosing and treating pets with hypoglycemia can be demanding and may require 24-hour care. Your primary care veterinarian may recommend referral to a specialty hospital where an ACVS board-certified veterinary surgeon and a veterinary internist are available, so advanced diagnostics, intensive care, and advanced surgery can be provided.

A definitive diagnosis of insulinoma is only made by biopsy obtained during surgery. Findings that support proceeding to surgery include:

• low blood glucose paired with simultaneously high blood insulin
• decreased blood fructosamine
• ultrasound or CT (CAT scan) evidence of a pancreatic mass

Management of insulinoma typically combines medical and surgical strategies.

Medical

Medical care focuses on increasing or stabilizing blood glucose using diet and medications.

• Diet: Nutritional management is critical. A high-fiber diet is often prescribed to slow sugar absorption. Offering small, frequent meals also helps prevent large glucose swings.
• Steroids: These drugs have multiple effects, including stimulating the liver to produce more glucose.
• Streptozocin: An antibiotic that selectively destroys pancreatic β-cells and/or β-cells at metastatic sites.
• Diazoxide: Reduces insulin secretion, promotes liver glucose production, and decreases cellular glucose use.
• Octreotide: Inhibits insulin synthesis and release.
• Glucagon infusion: A polypeptide hormone used to raise blood glucose by sustaining glucose production through glycogenolysis and gluconeogenesis; it may be used in hospitals to increase glucose until definitive therapy is possible.

Surgical

Surgery is essential for definitive diagnosis, staging, and treatment.

• The objective is to remove as much disease as possible by excising insulin-secreting masses, which commonly requires removing part of the pancreas. In many patients, this normalizes glucose for a period of time.
• During surgery, the veterinary surgeon also evaluates all abdominal structures for evidence of metastasis. Any additional masses found may be removed or biopsied depending on number, size, and location.

Most pets remain hospitalized 1–3 days after surgery. The most important aspect of recovery is rest. Pain medications are provided, and some surgeons also prescribe antibiotics. At home, the owner’s main tasks are ensuring the pet is eating and comfortable.

After removal of an insulin-secreting mass, blood glucose may temporarily become very high because the body has down-regulated insulin production and needs time to resume normal output. Manipulation of the pancreas can also trigger inflammation, leading to pancreatitis, which may cause vomiting, reduced appetite, and abdominal pain. In some cases, blood glucose remains low, suggesting residual microscopic disease. If hypoglycemia has been present for a long time, permanent nerve damage may exist, resulting in weakness or an uncoordinated gait.

Key concerns after surgery and medical therapy include metastasis, tumor regrowth, and recurrence of hypoglycemia signs. Dogs with a single surgically removed mass have the best prognosis, with survival typically about 1.5 years to a little over 2 years. Up to 80% of patients have a single mass. Dogs with normal or high blood glucose after surgery tend to do better than those with persistent hypoglycemia. Pets that already have metastatic disease at diagnosis generally have poorer outcomes, surviving about 7–9 months with combined surgical and medical management.